Deregulated mitochondrial metabolism is associated with a variety of hematopoietic disorders, including hematological malignancies. However, it remains poorly defined how mitochondrial metabolism coordinates hematopoietic cell development. Lack of such knowledge impedes understanding of and development of therapeutics for these diseases. In the previous funding period we demonstrated that PTPMT1, a Pten-like mitochondrial phosphatidylinositol phosphate phosphatase, plays a unique and crucial role in hematopoietic stem cells (HSCs). Deletion of PTPMT1 resulted in hematopoietic failure due to changes in the cell cycle and a complete block in the differentiation of HSCs. Strikingly, the absolute number of HSCs was increased by ~25-fold in the knockout mice. Moreover, although depletion of PTPMT1 from the entire hematopoietic system (including HSCs) caused hematopoietic failure and postnatal lethality, myeloid, T lymphoid, or B lymphoid lineage-specific knockout mice did not show any phenotypes, strongly suggesting that PTPMT1 is specifically important for stem cells, but not differentiated lineage progenitors. Mitochondrial aerobic metabolism of PTPMT1-depleted stem/progenitor (LSK) cells and lineage progenitors was decreased while cytosolic glycolysis was enhanced. Nevertheless, the detailed cellular and molecular mechanisms by which PTPMT1 deficiency alters cellular metabolism and profoundly deregulates stem cell activities remain to be determined. The objective of this renewal application is to further understand the metabolic regulation of HSCs by defining the role and acting mechanisms of PTPMT1. The central hypothesis is that PTPMT1 coordinates HSC activities (self-renewal, differentiation, and transformation) by controlling the balance between mitochondrial metabolism and cytosolic glycolysis. This hypothesis has been formulated on the basis of our work in the last funding cycle and recent preliminary studies. We plan to test our hypothesis and accomplish the objectives of this proposal by pursuing the following three aims. 1). To define the cellular mechanisms of the crucial role of PTPMT1 in hematopoiesis. 2). To determine the molecular mechanisms by which PTPMT1 deficiency reprograms cellular metabolism. 3). To investigate the role of PTPMT1 in leukemic transformation of stem cells and progenitors. The studies proposed in this application will greatly advance our understanding of how coordinated mitochondrial metabolism/bioenergetics, glycolysis, and glutaminolysis orchestrate HSC biology. These data will contribute to a much deeper understanding of the pathophysiology of blood disorders associated with deregulated mitochondrial function, which will help identify molecular targets for novel therapeutic interventions for these diseases.